An Inconvenient Truth exaggerated sea level rise

By Roger Highfield, Science Editor
Last Updated: 7:01pm BST 04/09/2008

Al Gore's Oscar-winning environmental documentary exaggerated the likely effects of global warming on sea levels, a new study shows.
The film, An Inconvenient Truth, suggested that the sea would rise up to 20ft "in the near future" as the ice in Greenland or Western Antarctica melts.

Other documentaries have picture Britain deluged with water, showing the House of Commons submerged.
However, while some mainstream predictions project sea levels 2 to 4 meters higher by 2100, a new study published today in Science concludes that a rise in sea level between 0.8 and 2 meters is much more likely.
While scientists agree that sea levels rose by six inches over the course of the 20th century, estimates of future rises remain hazy, mostly because there are many uncertainties, from the lack of data on what ice sheets did in the past to predict how they will react to warming, insufficient long-term satellite data to unpick the effects of natural climate change from that caused by man and a spottiness in the degree to which places such as Antarctica have warmed.
Prof Tad Pfeffer at University of Colorado in Boulder, Dr Joel Harper at University of Montana and Dr Shad O'Neel at Scripps Institute of Oceanography, La Jolla, reached these conclusions after studying the ice and water being discharged from Greenland and Antarctic ice sheets.
"We simply don't understand the physics of ice dynamics well enough to make accurate model predictions," says Dr Harper. "There are just too many uncertainties. So what we did is flip the problem on its head."
Unlike most past studies that try to add up the individual sources of ice and water discharge from the glaciers into the sea, their experiment calculated how much ice and water lost from Greenland and Antarctica that it would take for the world's seas to raise two meters.
Then they calculated how fast contributing glaciers would need to move in order to dump that much ice into the sea.
Their findings show that predictions of a two meter rise in sea level by 2100 would require significantly faster ice velocities from Greenland and Antarctica than has ever been reported before.
"We found you would need to have phenomenal calving, (calving is what happens when ice sheets meet the ocean and break apart to form icebergs)" said Dr Harper, who has lived and worked on the Greenland ice cap the past two summers, studying the increased melting there.
So if the glaciers continue to break up and melt like they are right now for 100 years, a two meter rise in sea level by 2100 would not be possible. For the Greenland ice sheet to do this, the glaciers moving into the island's calving fjords would have to increase their speed to 28.4 miles per year and sustain that speed until the end of the century.
For that reason, Prof Pfeffer and his colleagues argue that current projections of sea level rise should be updated to include more realistic rates of glacier break-up and melting in Greenland and Antarctica. They argue that their projection of as little as 0.8 meter rise in sea level by 2100 is much more realistic.
While the inflated rates often quoted by environmentalists are not completely out of the question, the authors argue that they should not be adopted as a central working hypothesis.
However, a rise of just a metre or more would wipe out the Norfolk Broads and the Wash, boosting the risk of devastating storm surges. And the new estimate does exceed that of thee latest Intergovernmental Panel on Climate Change report projects between 18 to 60 centimetres (7.2 to 24 inches) of sea level rise by 2100.
Dr David Vaughan of the British Antarctic Survey, commented: "while lower than a few of the wilder projections made by a fringe of activists, a rise of 0.8 to 2.0 metre in a century would cause enormous loss of life in the developing world and enormous cost in the developed world.
"These are big numbers, higher than the IPCC projections that governments generally use as the basis for policy-making."